Fuel cells are electrochemical generators which continuously, without direct combustion, convert gases such as H2 and O2 into electricity and heat by means of the electrochemical reactions taking place at electrodes separated by an electrolyte. For reasons essentially linked to operating reliability and to mass industrialization constraints, the choice of fuel cells comprising a solid electrolyte is particularly useful.
Currently, the two main types of solid-electrolyte fuel cells are proton-exchange membrane fuel cells (PEMFCs) and solid oxide fuel cells (SOFCs).
The main drawback of PEMFCs lies in the need to hydrate the proton-conducting membrane and in the poor thermal stability of the polymer materials, which limits the use of such cells to a temperature range lower than 120° C. and thus involves the use, in the electrodes, of expensive platinum-based catalysts that are susceptible to carbon monoxide poisoning.
The SOFC technology which involves operating at temperatures generally higher than 700° C. has numerous advantages compared with PEMFCs, such as a high electrical efficiency, often greater than 45%, the possibility of using carbon monoxide as fuel, of direct reforming and the absence of expensive catalysts. However, the high operating temperature of these cells induces a loss of long-term stability, a long start-up time and a low capacity for supporting thermal cycles. At issue for SOFCs is the reduction in the operating temperature in order to limit the degradation reactions at the interfaces, improve resistance to thermal cycling and thus increase the life of the cells.
There is therefore a need for fuel cells allowing the drawbacks of the systems described above to be overcome, i.e. solid-electrolyte fuel cells capable of operating at lower temperatures than SOFCs and less susceptible than PEMFCs to dehydration and carbon monoxide poisoning.